Numerous paper products are manufactured from fibers. These products are often manufactured from an aqueous slurry containing modified cellulose fibers derived from various plant sources. The slurry is formed in the wet end of a papermaking machine, where paper fiber is formed into a dilute water slurry and combined with a variety of materials before being distributed onto a paper machine wire. The water is subsequently removed from the slurry in a controlled manner to form a web, which is pressed and dried to create a finished paper product.
Additives can be incorporated into the slurry to enhance the papermaking process and to improve the finished papers' aesthetic and functional properties. These additives can include starch compositions incorporated during the wet end of the papermaking process to improve drainage and retention, to add strength, and to improve formation properties of the paper. Starch compositions can increase ink penetration times, reduce lateral spread of printing inks, and improve imaging and contrast. Starch compositions can also increase the surface integrity of papers, thereby decreasing picking in uses such as printing and photocopying.
Other ingredients that can be incorporated into paper are microparticles, including specialty clays, silica, and other functional fine particles. These microparticles are often added during the wet end of the papermaking machine. Depending upon the type of paper being made, as well as the characteristics of the slurry, various different microparticles can be added. One of the challenges of using microparticles during papermaking is that the microparticles are not all retained on the web as the paper is formed. The microparticles that are not retained often end up being discharged, which can be expensive because the particles are not used. Therefore, it is desirable to enhance particle retention.
Drainage, or de-watering ability, is another important consideration in the manufacture of paper because it is related to how fast a paper machine can remove water from the web. Typically, improved dewatering corresponds to higher speeds on paper machines and to higher production rates of paper. Papermakers often seek to retain all fiber and particulates on the wire at the greatest speed economically possible, without sacrificing product quality. However, papermakers often experience drainage limitations while trying to maintain product quality, and therefore it is desirable to have high drainage values such that the paper can be made at high speeds and high quality.
Although papermakers and suppliers of paper ingredients realize that high retention and drainage are desirable, a considerable challenge in making consistent, high-quality paper has been that papermaking systems are not all alike and can show significant variation. This variation can be the result of changes in the ingredients in the paper furnish as well as variability in the papermaking equipment. These variations can make it difficult to produce quality paper at high speeds due to changes in particle retention and drainage.
Presently, most ingredients added to the papermaking slurry are optimized for use under specific conditions. This is true, for example, of starch compositions added to the wet end of the papermaking process. Unfortunately, conditions at most papermaking facilities vary over time as the ingredients and systems change. Therefore, a need exists for improvements that allow for satisfactory drainage and particle retention over a range of papermaking conditions.